The Sigma 85mm f/1.4 DG HSM Art Lens offers a super-fast f/1.4 aperture that is great for getting images with an exceptionally shallow depth of field and smooth bokeh. It also uses two SLD elements, o espandi...ne anomalous partial dispersion/high-refractive index element, and one aspherical element that minimize aberrations and ensures a crisp, clear image. A Super Multi-Layer coating helps by suppressing flare and ghosting. A rounded 9-blade diaphragm also helps create round, smooth bokeh. It is made from a thermally-stable composite material that is light and durable and it has a brass bayonet mount.